Electrostatic filament dispersal for CMC

ABSTRACT

A method of preparing a woven fabric material for use in a ceramic matrix composite includes passing a desized woven fabric tape having a first inter-filament spacing through a dispersal module configured to transform the desized woven fabric tape into a dispersed woven fabric tape having a second inter-filament spacing greater than the first inter-filament spacing. The dispersal module includes a first charging element with a charged surface and disposed to apply an electric charge to the desized woven fabric tape. The method further includes applying a polymer binder to the dispersed woven fabric tape to create a stabilized woven fabric tape having the second inter-filament spacing.

BACKGROUND

The present invention relates to ceramic matrix composites, and moreparticularly, to the preparation of woven ceramic fabrics for use inceramic matrix composites.

In the processing of ceramic matrix composites (CMCs), there is a needto infiltrate matrix within and around tow bundles. In a woven CMCsystem, there are often large voids that exist between adjacent tows ofa preform that can become large defects after matrix infiltration. Suchdefects diminish interlaminar properties of the composite structure.Additionally, the inherent spacing between filaments of the tows andsubsequent preforming processes such as lay-up and debulking often causethe shape of these tows to contract, creating even larger defects andreducing surface contact area between plies. By dispersing theindividual filaments of the tows, the contact surface area between pliescan increase, resulting in a more homogenous pore distribution.

SUMMARY

A method of preparing a woven fabric material for use in a ceramicmatrix composite includes passing a desized woven fabric tape having afirst inter-filament spacing through a dispersal module configured totransform the desized woven fabric tape into a dispersed woven fabrictape having a second inter-filament spacing greater than the firstinter-filament spacing. The dispersal module includes a first chargingelement with a charged surface and disposed to apply an electric chargeto the desized woven fabric tape. The method further includes applying apolymer binder to the dispersed woven fabric tape to create a stabilizedwoven fabric tape having the second inter-filament spacing.

A system for processing a woven fabric material for use in a ceramicmatrix composite includes a dispersal module configured to transform adesized woven fabric tape into a dispersed woven fabric tape having asecond inter-filament spacing greater than the first inter-filamentspacing. The dispersal module includes a first charging element having acharged surface and disposed to apply an electric charge to the desizedwoven fabric tape. The system further includes an applicator downstreamof the dispersal module for applying a polymer material to the dispersedwoven fabric tape to create a stabilized woven fabric tape having thesecond inter-filament spacing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified illustration of a system used to prepare a wovenceramic fabric.

FIG. 2 is an enlarged cross-sectional view of a ceramic tow of the wovenceramic fabric showing the tow in a pre-dispersed (left) state and adispersed (right) state.

FIG. 3 is a flow chart illustrating steps of preparing the woven ceramicfabric for use in a ceramic matrix composite.

While the above-identified figures set forth one or more embodiments ofthe present disclosure, other embodiments are also contemplated, asnoted in the discussion. In all cases, this disclosure presents theinvention by way of representation and not limitation. It should beunderstood that numerous other modifications and embodiments can bedevised by those skilled in the art, which fall within the scope andspirit of the principles of the invention. The figures may not be drawnto scale, and applications and embodiments of the present invention mayinclude features and components not specifically shown in the drawings.

DETAILED DESCRIPTION

This disclosure presents a system and method for dispersing towfilaments within a woven ceramic fabric. An electric charge can beinduced in the woven fabric during processing such that individualfilaments within the tows disperse due to repulsion of like charges.Charging of the woven fabric can be accomplished using charged rollersor other conductive surfaces through/along which the fabric is passed.The dispersed fabric has a more uniform pore distribution to facilitatemore even infiltration with ceramic particles during densification.

FIG. 1 is a simplified illustration of system 10 used to disperse wovenfabric tape 12 prior to preforming and densification. FIG. 2 is asimplified cross-sectional view of a fiber tow 22 of woven fabric tape12. Tow 22 is shown in a pre-dispersed (left) and dispersed (right)state. FIG. 3 is a flowchart illustrating selected steps of method 100,used to prepare woven fabric tape 12 for use in a CMC. Steps 102-112 ofmethod 100 are described below in combination with FIGS. 1 and 2 . FIGS.1-3 are described together.

System 10 includes first charging element 14, optional air knife 16,second charging element 18, and applicator 20, through which wovenfabric tape 12 is passed in the direction indicated by arrows. In anexemplary embodiment, woven fabric tape 12 is formed from tows 22 ofbundled silicon carbide filaments 24. Other suitable ceramics arecontemplated herein. Tows 22 are preferably desized by a prior heattreatment or other suitable process to remove their polymer coatings inorder to enhance dispersal of filaments 24. Detensioning of woven fabrictape 12 may also be desirable to further enhance dispersal. Woven fabrictape 12 can be arranged in various weave patterns such as plain, harness(e.g., 3, 5, 8, etc.), twill, braid, or non-symmetric.

At step 102, woven fabric tape 12 is passed through first chargingelement 14. In the embodiment shown, first charging element 14 includescharged and grounded surfaces as charged rollers 26 and grounded rollers28. Each of charged rollers 26 and grounded rollers 28 can be formedfrom a metallic material, with charged rollers 26 also having anattached polymer or foam material for insulation and to preventgrounding. Charged rollers 26 could alternatively be formed from apolymer or glass material. In the illustrated embodiment, a friction pad30 abuts each charged roller 26 for the purpose of charging each chargedroller 26. In an alternative embodiment, friction pads 30 can be omittedif charged rollers 26 are charged in a manner other than by friction(e.g., via an applied electric current). Woven fabric tape 12 can passthrough charging element 14 in physical contact with grounded rollers28, while charged rollers 26 are offset from (i.e., not in physicalcontact with) woven fabric tape 12. Charged rollers 26 rotate in contactwith friction pads 30 to charge rollers 26. In the embodiment shown,friction creates negatively charged rollers 26. The negative chargeinduces a positive charge in woven fabric tape 12, causing adjacent tows22 and filaments 24 to disperse through repulsion of like charges. Assuch, woven fabric tape 12 exits first charging element 14 in adispersed state (i.e., dispersed woven fabric tape 12).

In an alternative embodiment, desized woven fabric tape 12 can becharged using a non-induction method. For example, first chargingelement 14 can be arranged as an electron gun or electrostatic generatorto charge desized woven fabric tape 12. First charging element 14 couldalternatively be formed from a polymer material and be disposed tofrictionally charge desized woven fabric tape 12 by rubbing against it.In such embodiments, a grounded surface may not be required. Othersuitable charging means are contemplated herein.

At step 104, a stream of air can optionally be applied to woven fabrictape 12 with air knife 16. Air knife 16 can be positioned to apply astream of air woven fabric tape 12 during or just after passing throughcharging element 14. Air knife 16 further disperses tows 22 throughmechanical means.

At step 106, woven fabric tape 12 can be collected by second chargingelement 18. Second charging element 18 can be arranged as two chargedsurfaces 32 disposed on opposite sides (i.e., top and bottom) of wovenfabric tape 12. For a positively charged woven fabric tape 12, chargingelement 18 can be negatively charged to further enhance the dispersedstate of woven fabric 12 as positively charged sub-elements (i.e., tows22 and filaments 24) are pulled toward one or the other of chargedsurfaces 32 as woven fabric tape 12 passes between surfaces 32. Secondcharging element 18 can also help dissipate the charge in woven fabrictape 12 before it undergoes subsequent processing.

In this regard, first charging element 14, optional air knife 16, andsecond charging element 18 act as a dispersal module to non-mechanically(through electrostatic repulsion) and mechanically (through an appliedstream of air) disperse and separate filaments 24 and tows 22 of wovenfabric tape 12. In alternative embodiments, the dispersal module caninclude any elements present (e.g., only charging elements 14 and 18)used for dispersing woven fabric tape 12.

The speed and extent to which woven fabric tape 12 is charged depends ona variety of factors, such as the number of charged rollers 26 and/orgrounded rollers 28, and/or the distance between charged rollers 26 andwoven fabric tape 12. Additionally, conditions of woven fabric tape 12can influence charging. For example, the thickness/number of filaments24 per tow 22 (e.g., ranging from 500 to 2,000), number of tows 22, andamount of residual polymer coating can all influence charging. It shouldalso be understood that the charge of rollers 26 can be reversed (i.e.,positive) such that a negative charge can be induced in woven fabrictape 12 without departing from the scope of this invention.

At step 108, dispersed woven fabric tape 12, which was previouslydesized and possibly detensioned to facilitate dispersal, can bestabilized in the dispersed state using a polymer binder to create astabilized woven fabric tape 12. Applicator 20 can be a source of apolymer binder material (e.g., conventional sprayer, electrostaticsprayer, bath, etc.). Exemplary polymer binders can include poly-vinylalcohol (PVA) or poly-vinyl butyral (PVB). Once the binder is applied,woven fabric tape 12 can be dried using heat or an air dryer if desired.

A dispersed/stabilized woven fabric tape 12 can differ from the originalwoven fabric tape 12 in several ways. First, repulsive electrical forcescause individual filaments 32 to push away from adjacent filaments,causing a “spreading out” of a tow 22, as shown in FIG. 2 . Adjacenttows 22 can experience similar repulsion and spreading. Accordingly,dispersed woven fabric tape 12 can have any of a greater number of tows12 due to spreading and regrouping of filaments 24 in smaller numbers,greater inter-filament spacing within a tow 22, and reduced inter-towspacing due to the increase in number of tows 22 and/or spreading oftows 22. For example, inter-filament spacing can double or triple fromthe original spacing. Additionally, the number of tows 22 in thedispersed woven fabric tape 12 can be two, three, or four times greater.It should further be understood that individual filaments 24 maydisperse in such a manner as to be grouped into more than one adjacenttow 22 along a length of the filament, such that tows 22 canintermingle.

At step 110, the stabilized woven fabric tape 12 can be cut into pliesand arranged into a desired two or three dimensional preform structure.Step 110 can also include localized application of ceramic particles toenhance regions of the preform structure.

At step 112, the preform structure can undergo matrix formation anddensification using a chemical vapor infiltration or deposition (CVI orCVD) process. During densification, the plies are infiltrated byreactant vapors, and a gaseous precursor deposits on the fibers. Thematrix material can be a silicon carbide or other suitable ceramicmaterial. Densification is carried out until the resulting CMC hasreached the desired residual porosity.

It may be desirable to control the environment surrounding system 10 tooptimize dispersal of woven fabric tape 12. Such an environment can, forexample, include a relatively low level of humidity and be generallyfree of contaminants such as dust or other particulates.

The dispersed woven ceramic fabric formed using method 100 has moreevenly distributed surface area for receiving ceramic particles duringinfiltration due to the spreading of filaments and tows allowing formore robust matrix formation. Infiltration time may also be reduced asthe vapors can more easily penetrate the increased size offilament-to-filament pores. The resulting CMC formed with the wovenfabric can be incorporated into aerospace, maritime, or industrialequipment, to name a few, non-limiting examples.

Discussion of Possible Embodiments

A method of preparing a woven fabric material for use in a ceramicmatrix composite includes passing a desized woven fabric tape having afirst inter-filament spacing through a dispersal module configured totransform the desized woven fabric tape into a dispersed woven fabrictape having a second inter-filament spacing greater than the firstinter-filament spacing. The dispersal module includes a first chargingelement with a charged surface and disposed to apply an electric chargeto the desized woven fabric tape. The method further includes applying apolymer binder to the dispersed woven fabric tape to create a stabilizedwoven fabric tape having the second inter-filament spacing.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

In the above method, the woven fabric material can include siliconcarbide.

In any of the above methods, the dispersal module can further include asecond charging element downstream of the first charging element, andpassing the desized woven fabric tape through the dispersal module caninclude passing the desized woven fabric tape sequentially though thefirst and second charging elements.

In any of the above methods, the charged surface of the first chargingelement can have the same electric charge as the second chargingelement.

In any of the above methods, the first charging element can furtherinclude a grounded surface in physical contact with the desized wovenfabric tape.

In any of the above methods, the grounded surface can include aplurality of grounded rollers.

In any of the above methods, the charged surface can include a pluralityof charged rollers physically spaced apart from the desized woven fabrictape.

Any of the above methods can further include forming the stabilizedwoven fabric tape into a plurality of plies, laying up the plurality ofplies to form a preform, and densifying the preform.

In any of the above methods, the step of densifying the preform caninclude one of a chemical vapor infiltration and a chemical vapordeposition process.

A system for processing a woven fabric material for use in a ceramicmatrix composite includes a dispersal module configured to transform adesized woven fabric tape into a dispersed woven fabric tape having asecond inter-filament spacing greater than the first inter-filamentspacing. The dispersal module includes a first charging element having acharged surface and disposed to apply an electric charge to the desizedwoven fabric tape. The system further includes an applicator downstreamof the dispersal module for applying a polymer material to the dispersedwoven fabric tape to create a stabilized woven fabric tape having thesecond inter-filament spacing.

The system of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

In the above system, the woven fabric material can include siliconcarbide.

In any of the above systems, the charged surface can include a pluralityof charged rollers physically spaced apart from the desized woven fabrictape.

In any of the above systems, the first charging element can furtherinclude a grounded surface in physical contact with the desized wovenfabric tape.

In any of the above systems, the grounded surface can include aplurality of grounded rollers.

In any of the above systems, the plurality of grounded rollers and theplurality of charged rollers can be formed from a metallic material.

In any of the above systems, the plurality of charged rollers canfurther be formed from an insulating material.

In any of the above systems, the dispersal module can further include asecond charging element downstream of the first charging element.

In any of the above systems, the second charging element can include apair of charged surfaces having an opposite electric charge from thedispersed woven fabric tape.

In any of the above systems, the polymer material can be one ofpoly-vinyl alcohol (PVA) and poly-vinyl butyral (PVB).

In any of the above systems, the applicator can be a conventional orelectrostatic sprayer.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A method of preparing a woven fabricmaterial for use in a ceramic matrix composite, the method comprising:passing a desized woven fabric tape having a first inter-filamentspacing through a dispersal module configured to transform the desizedwoven fabric tape into a dispersed woven fabric tape having a secondinter-filament spacing greater than the first inter-filament spacing,the dispersal module comprising: a first charging element disposed toapply an electric charge to the desized woven fabric tape, the firstcharging element comprising a charged surface; and applying a polymerbinder to the dispersed woven fabric tape to create a stabilized wovenfabric tape having the second inter-filament spacing.
 2. The method ofclaim 1, wherein the woven fabric material comprises silicon carbide. 3.The method of claim 1, wherein the dispersal module further comprises asecond charging element downstream of the first charging element, andwherein passing the desized woven fabric tape through the dispersalmodule comprises passing the desized woven fabric tape sequentiallythough the first and second charging elements.
 4. The method of claim 3,wherein the charged surface of the first charging element has the sameelectric charge as the second charging element.
 5. The method of claim1, wherein the first charging element further comprises a groundedsurface in physical contact with the desized woven fabric tape.
 6. Themethod of claim 5, wherein the grounded surface comprises a plurality ofgrounded rollers.
 7. The method of claim 6, wherein the charged surfacecomprises a plurality of charged rollers physically spaced apart fromthe desized woven fabric tape.
 8. The method of claim 1, and furthercomprising: forming the stabilized woven fabric tape into a plurality ofplies; laying up the plurality of plies to form a preform; anddensifying the preform.
 9. The method of claim 8, wherein the step ofdensifying the preform comprises one of a chemical vapor infiltrationand a chemical vapor deposition process.
 10. A system for processing awoven fabric material for use in a ceramic matrix composite, the systemcomprising: a dispersal module configured to transform a desized wovenfabric tape into a dispersed woven fabric tape having a secondinter-filament spacing greater than the first inter-filament spacing,the dispersal module comprising: a first charging element disposed toapply an electric charge to the desized woven fabric tape, the firstcharging element comprising a charged surface; and an applicatordownstream of the dispersal module for applying a polymer material tothe dispersed woven fabric tape to create a stabilized woven fabric tapehaving the second inter-filament spacing.
 11. The system of claim 10,wherein the woven fabric material comprises silicon carbide.
 12. Thesystem of claim 10, wherein the charged surface comprises a plurality ofcharged rollers physically spaced apart from the desized woven fabrictape.
 13. The system of claim 12, wherein the first charging elementfurther comprises a grounded surface in physical contact with thedesized woven fabric tape.
 14. The system of claim 13, wherein thegrounded surface comprises a plurality of grounded rollers.
 15. Thesystem of claim 14, wherein the plurality of grounded rollers and theplurality of charged rollers are formed from a metallic material. 16.The system of claim 15, wherein the plurality of charged rollers arefurther formed from an insulating material.
 17. The system of claim 10,wherein the dispersal module further comprises a second charging elementdownstream of the first charging element.
 18. The system of claim 17,wherein the second charging element comprises a pair of charged surfaceshaving an opposite electric charge from the dispersed woven fabric tape.19. The system of claim 10, wherein the polymer material is one ofpoly-vinyl alcohol (PVA) and poly-vinyl butyral (PVB).
 20. The system ofclaim 10, wherein the applicator is a conventional or electrostaticsprayer.